1. Field of the Invention
The invention relates in general to cyanine dyes mixture for optical recording media.
2. Description of the Related Art
A storage medium with higher storage density, smaller size and lower cost is extremely required now-a-days. As magnetic storage medium is not able to satisfy these requirements, optical storage material is greatly sought for as an alternative. It is found that organic dye which combines the advantages and characters of both the photosensitizer and photorecording medium, is highly developed and adopted for optoelectronic industry. The applications of organic dye include in the fields of, for example, nonlinear optical device, recording and displaying of optical disc data, photoresist, sensor and indicator for heat, light, and electron, during the transfer and storage of energy, medicine and biology, etc. The cyanine dyes mixture of this invention has high absorption coefficient in the infrared region which implies that the cyanine dye has high recording sensitivity and signal to noise ratio (S/N) value. Therefore, cyanine dyes mixture is an ideal optical memory storage material.
An organic dye, cyanine blue, was first synthesized by Greville Williams in 1856 (K. Venkataraman (ed.), The Chemistry of Synthetic Dyes, Vol.II, p.1143-1186, Academic Press, New York, 1952). In 1875, Vogel discovered that cyanine blue has special photosensitizing properties. Therefore, cyanine blue, which was originally used as colorant, turned to be a photosensitizer with higher added value. Different structures of cyanine dye have different .lambda.max which varies from UV to IR. Therefore, cyanine dye can also serve as photosensitizer for photoresist or optical storage medium in electronic industry besides a colorant.
Cyanine dye, 3,3'-diethyl-12-acetyl-thiatetracyanine perchlorate, was first proposed for application in optical disc fabrication by Law et al. (K. Y. Law, P. S. Vincett, and G. E. Johnson, Appl. Phys. Lett., 39, 718 (1981)). The cyanine dye and PVAc (poly(vinyl acetate)) were first mixed and then spin-coated to form an optical recording medium. After this successful application, several kinds of cyanine dye were developed for optical disc applications, such as those disclosed in U.S. Pat. Nos. 5,019,476, 5,292,615, 5,328,802, 5,332,608, 5,424,171 and 5,455,094, etc. As to the method of fabrication, it is found that spin coating of the dye on the substrate can shorten the process and reduce the cost as compared to the chemical vapor deposition (CVD) process; therefore spin coating is accepted as the standard procedure, and the stability of the organic dye and its solubility to organic solvent are critical factors for successful applications.